The invention pertains to a device for determining the angular position of the steering wheel of a motor vehicle.
The steering angle or the steering angle lock of motor vehicles is needed to apply to a driving dynamics control system, for example. Now this kind of driving dynamics control system receives the aforementioned steering angle value, in addition to other measured data, such as the wheel velocities or the rotation of the motor vehicle about its vertical axis. But the absolute steering angle lock and also the steering velocity are needed so that these values, together with the other measured data, can be evaluated by the driving dynamics system and then used to control actuators, for example, the brakes and/or the drive force transmission.
Steering angle sensors are available in a number of different designs using different measuring principles. For example, from DE 43 00 663 C1, a steering angle sensor is known in which light barriers are distributed along the perimeter for sensing of a code placed on an aperture ring. With this sensor it is possible to ascertain the absolute angular setting relative to one complete revolution of the steering wheel.
Likewise relative to one full revolution, the optical-electronic steering angle sensor known from DE 40 22 837 A1 measures the angular position of the steering wheel. The steering angle sensor disclosed in this document consists of two elements positioned in parallel and at a distance to each otherxe2x80x94one is a light source and the other is a line sensorxe2x80x94and also a code disk located between the light source and the line sensor; said code disk is connected to and rotates with the steering wheel spindle. A CCD sensor is used as the line sensor in this case. The code generator is designed as a light slit disk and for its code track it uses a spiral increasing in size from inside to outside. By means of the lighting of the image points of the cell sensor at a particular steering lock, it is possible to obtain information about the actual steering angle lock.
As coding for this code disk, an archimedean spiral extending across 360xc2x0 is used. With this steering angle sensor, it is possible to determine absolute steering wheel angular settings only in the range of the coding, so that there, too, the operation is limited to a range of 360xc2x0. Steering wheels of motor vehicles, however, can be rotated by far more than 360xc2x0. Proceeding from a straight positioning of the wheels and thus a zero setting of the steering angle sensor, it is desirable to determine the steering angle accurately in an angular range that covers the entire rotational range of the steering wheel. With the known steering angle sensor, in this regard it is possible only to determine an angular segment, namely in the range of one complete steering wheel lock of 180xc2x0 to the right and accordingly, 180xc2x0 to the leftxe2x80x94proceeding from the zero setting of the steering wheel. Steering wheels of motor vehicles can turn, for example, three full rotations to the right and accordingly also three full rotations to the leftxe2x80x94starting from the zero positionxe2x80x94so that a total range of 2160xc2x0 would have to be measured by a steering angle sensor.
Known solutions to this problem rely on mechanical elements for determining the completed, full revolutions of the steering wheel. This kind of mechanical design is described, e.g., in DE 196 01 965 A1, wherein a 360xc2x0 optical-electronic sensor is described which is supplemented with a mechanical counter for the revolutions. Based on the mechanical translation gearing used in this device, with this design we in turn lose the advantages of contactless sensor technology, such as non-wear and low-noise attributes.
One possible design using a contactless measuring principle is described in DE 198 35 886 A1, wherein a device to determine the steering angle is disclosed. This device uses a variable inductivity as a measure for the absolute angular setting of the steering wheel even for several revolutions. This variable inductivity is formed by a flat ribbon located between a rotor and an outer housing surrounding it and is designed as a kind of clock spring.
The determination of an inductivity, however, thus necessitates, firstly, a complicated electronic measuring device, and secondly, as shown by the measured results presented in FIGS. 4 to 7 of this patent disclosure, the method selected there is affected by some very large fluctuations in measured values and thus is affected by considerable inaccuracies in the output of the angular value.
Conversely, the present invention is based on the goal of proposing a steering angle sensor for determining the absolute angular position of the steering wheel of a motor vehicle which likewise has a measured range going beyond 360xc2x0, and which is able to achieve more accurate measured results with simple electronic devices and without additional mechanical expense.
This is achieved by the use of a measuring device with at least one coil device which cooperates with an electrically conducting structure implemented on/in a flexible flat ribbon, where the flexible flat ribbon cable is wound up in a winding gap bounded by the outer mantle surface of the inner rotor and the inner mantle surface of the exterior stator positioned at a distance to it, in such a manner that its one end is attached to the rotor and its other end is attached to the stator.
In a first design embodiment, a transmission composed of two magnetically linked coil devices is provided, wherein one of the two coil devices is formed at least by a circuit path extending on/in the flat ribbon cable along its longitudinal axis, and the other coil device is designed as a transmission coil provided for induction of a measuring voltage in the first coil device and is positioned coaxially to the stator and is mechanically connected to it.
In this case, it is favorable if the coil designed as a transmission coil, located coaxial to the stator, is connected electrically to a circuit generating a high-frequency alternating current.
One particularly simple mechanical structure can be obtained when the coil designed as transmission coil and positioned coaxial to the stator is designed by means of circuit path structures printed on an electronic circuit board.
The return of the measured signal from the rotor to the stator side takes place in this design format, preferably by a capacitive coupling or by means of an electrically conducting steering wheel spindle.
In yet another design, the coil surface of the at least one coil device is aligned in parallel with the mantle surface of stator and rotor.
Another refinement of this design provides that, due to the circuit path structure implemented on/in the flat ribbon cable, a coil device is formed which, together with the first coil device, forms a transmission, where the steering angle between the two coil devices is determined by the angular position of the steering wheel.
One of the two coil devices can be designed, e.g., as an electrically conducting structure applied to one mantle surface of the stator.
The flat ribbon cable can be positioned in such a manner that the flat ribbon cable is coiled up in a spiral shape with the same sense of direction persisting across its entire length in any rotor position, and in the two end positions of the rotor rotation, on the one hand it rests almost completely against the outer mantle surface of the rotor, and on the other hand it rests almost completely against the inner mantle surface of the stator.
As an alternative to this, the flat ribbon cable is coiled up so that in the middle position of the steering wheel, one section thereof is coiled in one direction resting against the outer mantle surface of the rotor, and an additional section is coiled up in the opposing direction resting against the inner mantle surface of the stator, so that a loop reversing the coil direction is formed between the two sections.
One particularly preferred use of one of these devices is for determining the angular position of the steering wheel in a steering column or steering wheel unit in which a coil spring cassette is used for transmission of electrical current between the steering column as stator, and the steering shaft as rotor. In this kind of coil spring cassette, the power-transmission lines are combined in one or more flat ribbon cables, which are wound up in the winding gap formed by rotor and stator. In addition to these existing electrical circuit paths, additional ones can be provided at no great expense for the determination of the angular position of the steering wheel according to this invention, provided that the existing lines cannot be used for this purpose, e.g., by separation and filtering of the signals in the frequency range.
It is also favorable to use one of the described devices in combination with an additional steering angle determining device which features a more limited measuring range with respect to the existing device, but which instead has a greater resolution, for simultaneous determination of the absolute value of the steering angle by use of a coarse and a fine determination.